OverTwitter

Inspired by the @abovelondon Twitter feed that reports upcoming visible transits of interesting objects over the UK’s capital city, I have created several similar Twitter feeds. It began with @overcardiff, a feed covering my own home city, but then I have since taken requests for other places all over the planet. Here’s the lowdown on which feeds are available, how to request a new one and what they say.

What will these Twitter feeds tell me? These feeds determine when the International Space Station (ISS), Hubble, Envisat and other interesting objects will be visible in the relevant location. They will also alert you to bright Iridium flares; elusive, momentary flashes of reflected light from the Iridium constellation of satellites. These can be often be seen in daylight! When the time approaches, an alert appears on the Twitter feed. You will get 30-45 minutes warning on the sighting opportunity.

What cities are covered so far? So far there are Twitter feeds for . If you live within 20 miles of one of these cities, the data in the feed will still be correct for your location. Within 50 miles of one of these cities then the data will still be only a minute out in most cases. Tweet alerts only appear when the weather in your location is good enough to allow the transit to be seen. The weather data comes from Yahoo! Weather. Each tweet gives the same information, for example below is a tweet from the @oversydney feed.

The ISS will pass over Sydney at mag -1.7 at 4:32am on January 25th. Moves from 46deg elevation SW to 10deg elevation SE over 3 min.

The mag number refers to the brightness of the object on the magnitude scale, the lower the better. After that comes a pair of coordinares on the sky – the beginning and end of the track the object will make. ’46deg elevation’ means it will be 46 degrees above the horizon (where 90 degrees is directly overhead). SW and SE are Southwest and Southeast compass directions around the horizon. The duration of visibility is given as ‘3 min’.

How do I get a feed for my location? If you would really like a feed for a city near you, then feel free to email me or contact me via Twitter (@orbitingfrog). The next time I get around to adding more locations, I shall try to include your request.

RSS Feeds Alternatively, you can subscribe to an XML (RSS 2.0) feed for visible transits in any location! Use the map below to find your location and/or drag the red marker to the right place. Click ‘Get RSS’ and the RSS feed will be loaded in a new browser window. Or if you know your latitude and longitude, you can simply point your RSS feed reader to

I'm Robert Simpson and I work at Google in London. I am the creator of <a href="http://dotastronomy.com">.Astronomy</a>. I am astrophysicist formerly of the <a href="http://zooniverse.org">Zooniverse</a> at the University of Oxford.